In Pokémon Black & White, like the past games, the trainer card changes colour based upon the various achievements you have accomplished within the game. There are six different colours for the Trainer Card, each dependant on the amount of Stars on your card. The colours are as follows

Start

Stage 1

Stage 2

Stage 3

Stage 4

Stage 5

Green

Purple

Red

Silver

Gold

Black/White

These changes are done by following these instructions in any order.

Defeat the Elite Four

Complete National Dex

Collect all Pokémon Musical goods

Obtain all Entralink powers

Get a 49 streak in both Super Single and Super Double lines in the Battle Subway.

The Trainer Card - Front & Back

First, the Trainer card now has a new option where you can select your trainer nature. On the front, you'll get details on the amount of Pokémon you have seen in your Pokédex as well as the amount of money you have on you in the game. On the back, you get your ID number, the game time and the date you began your Pokémon journey.

In addition to that, you have a signature strip which you can write on. You have the ability to zoom in on this part and you can even make a two frame animation out of the two halves of the signature strip.

The Trainer Card - Badges

In addition to the trainer card, you have the option to open and view your badge case. Like the badges in Pokémon Diamond, Pearl & Platinum, you have the ability to tap these badges and with that, you can polish them so they have a nice glint on them.

When you select the badge, you get a view of the Gym Leader as well as details on what the badge unlocks and the date in which you defeated the Gym Leaders.